Defining the ATA-2025 'consider RAIT' zone in older patients with N1b PTC

The aim of this study was to quantify the cancer-specific death (CSD) benefit of radioactive iodine therapy (RAIT) in older patients with N1b differentiated thyroid carcinoma, a population designated by the ATA-2025 guideline as a 'consider RAIT' zone despite unproven mortality benefit, and to translate this recommendation into clinically actionable subgroups using a competing-risks framework. We used data from the Surveillance, Epidemiology, and End Results (SEER) programme (2004-2015) and analysed papillary thyroid carcinoma (PTC) cases aged ≥55 years with N1b, M0. After 1:1 propensity score matching, cumulative incidence function and Fine-Gray models evaluated associations between RAIT and CSD. Stratifications included tumour size, positive lymph node burden (PLN > 5), and ETE. A nomogram was developed for 1-, 3-, and 5-year CSD prediction, and absolute risk reduction (ARR) and number needed to treat (NNT) were estimated. Among 1,142 patients, 648 were matched (n = 324/group; median follow-up = 69 months). Five-year CSD was 14.1% without RAIT versus 5.1% with RAIT (P = 0.001), yielding ARR ≈ 9% and NNT ≈ 11. RAIT was independently protective (SHR 0.33, 95% CI: 0.14-0.76). Benefit concentrated in tumours 2-4 cm, PLN > 5, and ETE-positive strata. The nomogram showed strong discrimination and calibration. In patients aged ≥55 years with N1b PTC, RAIT confers measurable mortality benefit, most evident in 2-4 cm, PLN > 5, or ETE-positive disease. Integrating ARR, NNT, and a validated nomogram, this study converts the conceptual 'consider RAIT' into clinically actionable 'RAIT-favoured' and 'RAIT-optional' pathways.